Prick the sausages, put into a medium non-stick saucepan with the oil and cook on a medium heat. Meanwhile, peel and slice the onion and garlic, then add to the pan.
If you’re using fresh mushrooms, clean and slice them; if you’re using tinned ones, drain them. When the sausages have browned all over, add the mushrooms and continue cooking for a few minutes. Then pour in the beer and chopped tomatoes, add the herbs and stir everything together.
Reduce the heat to low and cook for 30 minutes, stirring occasionally to prevent it sticking to the bottom of the pan.
To make this go further, add a tin of white beans. I rinse the sauce from a can of baked beans, but any tinned white beans – haricot, cannelini, butter beans – will do. Replace the beer with red or white wine if you have it – red wine for a deep, rich flavour, white for a lighter, sweeter dish.